Motor-vehicle gearbox

Abstract

The gearbox comprises an engagement sleeve movable between a neutral position and one engagement position for engagement of one given gear, and a shift fork operatively connected to the engagement sleeve for controlling the movement thereof between the neutral position and the engagement position. The shift fork is slidably mounted on a stationary support rod, which is provided with a pair of bushes defining a first axial abutment surface for stopping the movement of the shift fork in the direction from the neutral position to the engagement position and a second axial abutment surface for stopping the movement of the shift fork in the direction from the engagement position to the neutral position. The neutral position of the shift fork is axially spaced from the second axial abutment surface.

1. Motor-vehicle gearbox comprising:
 an engagement sleeve movable between a neutral position and one engagement position for engagement of one given gear, 
 a sliding shift fork operatively connected to the engagement sleeve for controlling the movement thereof between the neutral position and the engagement position, 
 a linear hydraulic actuator having a plunger, wherein the plunger is connected to the shift fork for controlling the translational movement thereof and has three positioning notches equally spaced in the sliding direction of the plunger, 
 a linear position sensor able to provide a signal indicative of the position of the plunger of the linear hydraulic actuator, 
 a position-marking ball adapted to engage alternatively in one of the three positioning notches to hold the engagement sleeve in the neutral position or in the engagement position, 
 a first axial abutment surface for stopping the movement of the shift fork in the direction from the neutral position to the engagement position and a second axial abutment surface for stopping the movement of the shift fork in the direction from the engagement position to the neutral position, 
 wherein in the neutral position the shift fork is axially spaced from the second axial abutment surface by a distance which is larger than the sensibility of the linear position sensor, but smaller than the travel the plunger must run in order for the position-marking ball to shift from the positioning notch corresponding to the neutral position to the adjacent positioning notch. 
 
     
     
       2. Gearbox according to  claim 1 , comprising a stationary support rod on which the shift fork is mounted. 
     
     
       3. Gearbox according to  claim 2 , further including first and second bushes mounted on the support rod, wherein the first bush defines the first axial abutment surface and the second bush defines the second axial abutment surface. 
     
     
       4. Gearbox according to  claim 3 , wherein the shift fork includes a pair of support plates each having a respective guide through hole, of which the one guide through hole is provided with a guide bush and is guided along the support rod and the other guide through hole is guided along a portion of the first bush. 
     
     
       5. Gearbox according to  claim 4 , wherein the first bush comprises a first, axially inner bush portion and a second, axially outer bush portion, wherein the first bush portion has a smaller diameter than the second bush portion, wherein the guide through hole of said shift fork is guided along the first bush portion and wherein the second bush portion forms the first axial abutment surface. 
     
     
       6. Gearbox according to  claim 4 , wherein the first bush and the guide bush are made of plastics. 
     
     
       7. Gearbox according to  claim 6 , wherein the guide bush is obtained by overmoulding over said shift fork.